You’ve just scored an interview for a React JS position – the job of your dreams. You’re feeling pretty confident about your React skills, but there’s that nagging worry about interview questions. Will you be able to answer them like a pro? It’s a problem that keeps many up at night. If you are facing this problem, we have just what you need! In this article, we are going to discuss the top 25+ React JS interview questions and answers.
By the end of this guide, you’ll not only have the answers but also the confidence to ace the interview.
Basic React JS Interview Questions
Here are some basic level React interview questions and answers:
1. What is React, and why is it popular?
React is a JavaScript library used for building user interfaces. It’s popular because it provides a component-based structure, making it easier to develop and maintain complex UIs.
2. What are the advantages of using React?
- It provides better performance due to its virtual DOM.
- It is easy to learn and use.
- It supports server-side rendering.
3. What is JSX, and how is it different from HTML?
JSX (JavaScript XML) is a syntax extension for JavaScript used in React. It allows you to write HTML-like code within JavaScript, making it easier to create React elements.
4. What are props in React?
Props (short for properties) are used to pass data from parent to child components. They make it possible to configure child components and make them reusable.
5. Differentiate between class components and functional components.
Class components use ES6 classes for defining a component, while functional components are defined as JavaScript functions. With the introduction of Hooks, functional components can also manage state.
6. Explain the virtual DOM in React.
The virtual DOM is a lightweight copy of the actual DOM. React uses it to optimize updates, reducing the need to directly manipulate the real DOM, which can be slow.
React JS Interview Questions and Answers for Freshers
Here are some important React interview questions for freshers:
7. Explain the concept of state in React.
A state is an object that stores data that can be used to render a component. When state changes, React re-renders the component to reflect those changes.
8. How do you create a React component?
You can create a React component by extending the React.Component class (class component) or by defining a function that returns JSX (functional component). Both approaches are valid, but functional components are preferred for simplicity.
9. What is the purpose of the setState method in React?
The setState method is used to update the state of a React component. When you call setState, React schedules a re-render of the component, reflecting the new state. It’s the primary way to update the UI in response to user actions or data changes.
10. Explain the concept of props drilling in React.
Prop drilling, also known as prop passing, occurs when you need to pass data from a parent component to a deeply nested child component. This can lead to passing props through several intermediate components. To avoid this, you can use React Context API or state management libraries like Redux.
11. How do you handle events in React?
In React, you can handle events by using event handlers. For example, you can use the onClick attribute to define a click event handler. Event handlers are typically defined as functions within the component and can be used to modify the component’s state.
12. What is the significance of keys in React lists?
Keys are used to help React identify which items have changed, added, or removed from a list. They assist in efficient updates and reconciliation.
React JS Advanced Interview Questions
Here are some important React advanced interview questions and answers:
13. What is the significance of React Fiber?
React Fiber is a reimplementation of the React reconciliation algorithm. It allows React to prioritize and interrupt rendering to make applications more responsive. Fiber reconciles the virtual DOM in a more granular way, enabling features like concurrent mode and improved performance.
14. Explain the concept of Higher Order Components in React.
HOCs are a design pattern in React that allows you to reuse component logic. They are functions that take a component and return a new component with additional props and behavior. HOCs are often used for sharing code between components, such as for authentication or data fetching.
15. What is Redux, and how does it work with React?
Redux is a predictable state container for managing the global state of a React application. It provides a central store to hold application data, and components can access and modify this data by dispatching actions. Redux works seamlessly with React by using the React-Redux library to connect the store to React components.
16. What is a React Router, and how do you achieve client-side routing in a React application?
React Router is a library for handling client-side routing in React applications. It allows you to define routes and render components based on the URL. You can achieve client-side routing by installing and configuring React Router and defining routes using components like Route and BrowserRouter.
17. What are hooks in React, and why are they important?
React hooks are functions that allow functional components to use state and other React features previously available only in class components. They include useState, useEffect, useContext, and more. Hooks simplify component logic and make it more reusable and maintainable.
18. How does React’s Context API work, and when should you use it?
React’s Context API provides a way to pass data down the component tree without explicitly passing props at every level. It’s useful for sharing data like user authentication or theme preferences. Use it when data needs to be accessible by multiple components without prop drilling.
React JS Interview Questions for Experienced
Here are some important ReactJS interview questions and answers for experienced:
19. What are the key differences between React class components and functional components, and when would you choose one over the other in a project?
Class components use ES6 classes, support state lifecycle methods, and are ideal for complex logic. Functional components are simpler, stateless, and support Hooks for state management. Choose class components for legacy code or specific use cases, but functional components are preferred for new projects.
20. Explain the concept of code-splitting in React. How does it improve performance, and what tools can be used for code-splitting?
Code-splitting is a technique that divides a JavaScript bundle into smaller, separate files. This reduces the initial load time of a web application, as only necessary code is fetched when needed. React supports code-splitting using tools like Webpack, React.lazy, and Suspense.
21. How do you handle server-side rendering (SSR) in a React application? Can you describe the steps involved in setting up SSR?
Setting up SSR involves configuring a server (Node.js) to render React components on the server and send the initial HTML to the client. Key steps include using libraries like Express, implementing routing, and ensuring data fetching on the server side. Popular libraries like Next.js simplify this process.
22. Explain how you can optimize the performance of a React application. Mention techniques, tools, and best practices you’d use for optimization.
Performance optimization in React involves techniques like code-splitting, lazy loading, minimizing unnecessary renders, using memoization, and optimizing images. Tools like React DevTools, Webpack, and service workers are used to analyze and improve performance.
23. What are the key principles of the Redux architecture, and how can you manage complex states with Redux in a React application?
Redux follows the principles of a single source of truth, a read-only state, and changes through pure functions. You can manage complex states by creating a central store, defining action reducers, and connecting components to the store using the connect function or React-Redux. This ensures a predictable and maintainable state management system.
ReactJS Coding Interview Questions
Here are some important coding React JS questions and answers:
24. Write a React component that fetches data from an API and displays it. Use the useEffect hook and handle loading and error states.
import React, { useState, useEffect } from ‘react’;
function DataFetchingComponent() {
const [data, setData] = useState(null);
const [loading, setLoading] = useState(true);
const [error, setError] = useState(null);
useEffect(() => {
fetch(‘https://api.example.com/data’)
.then((response) => response.json())
.then((data) => {
setData(data);
setLoading(false);
})
.catch((error) => {
setError(error);
setLoading(false);
});
}, []);
if (loading) return <div>Loading…</div>;
if (error) return <div>Error: {error.message}</div>;
return (
<div>
<h1>Data from API:</h1>
<pre>{JSON.stringify(data, null, 2)}</pre>
</div>
);
}
export default DataFetchingComponent;
25. Create a controlled input component in React. Handle its value and onChange event.
import React, { useState } from ‘react’;
function ControlledInput() {
const [inputValue, setInputValue] = useState(”);
const handleInputChange = (event) => {
setInputValue(event.target.value);
};
return (
<div>
<input
type=”text”
value={inputValue}
onChange={handleInputChange}
/>
<p>Value: {inputValue}</p>
</div>
);
}
export default ControlledInput;
26. Implement a simple toggle button in React that changes its state when clicked.
import React, { useState } from ‘react’;
function ToggleButton() {
const [isToggled, setIsToggled] = useState(false);
const handleToggle = () => {
setIsToggled(!isToggled);
};
return (
<div>
<button onClick={handleToggle}>
{isToggled ? ‘Toggle Off’ : ‘Toggle On’}
</button>
</div>
);
}
export default ToggleButton;
27. Create a React component that renders a list of items from an array, including the ability to remove items from the list.
import React, { useState } from ‘react’;
function ListWithRemoval() {
const [items, setItems] = useState([‘Item 1’, ‘Item 2’, ‘Item 3’]);
const handleRemoveItem = (index) => {
const updatedItems = […items];
updatedItems.splice(index, 1);
setItems(updatedItems);
};
return (
<ul>
{items.map((item, index) => (
<li key={index}>
{item}
<button onClick={() => handleRemoveItem(index)}>Remove</button>
</li>
))}
</ul>
);
}
export default ListWithRemoval;
28. Create a React component that allows users to drag and reorder a list of items.
Implementing drag-and-drop functionality can be more involved and often requires the use of external libraries like react-beautiful-dnd or react-dnd.
Example of a basic drag-and-drop component.
Implementing full drag-and-drop functionality would require additional code.
import React, { useState } from ‘react’;
import { DragDropContext, Draggable, Droppable } from ‘react-beautiful-dnd’;
const initialItems = [
{ id: ‘item-1’, content: ‘Item 1’ },
{ id: ‘item-2’, content: ‘Item 2’ },
{ id: ‘item-3’, content: ‘Item 3’ },
];
const DragAndDropList = () => {
const [items, setItems] = useState(initialItems);
const onDragEnd = (result) => {
if (!result.destination) return; // dropped outside the list
const updatedItems = Array.from(items);
const [reorderedItem] = updatedItems.splice(result.source.index, 1);
updatedItems.splice(result.destination.index, 0, reorderedItem);
setItems(updatedItems);
};
return (
<DragDropContext onDragEnd={onDragEnd}>
<Droppable droppableId=”droppable”>
{(provided) => (
<ul {…provided.droppableProps} ref={provided.innerRef}>
{items.map((item, index) => (
<Draggable key={item.id} draggableId={item.id} index={index}>
{(provided) => (
<li
ref={provided.innerRef}
{…provided.draggableProps}
{…provided.dragHandleProps}
>
{item.content}
</li>
)}
</Draggable>
))}
{provided.placeholder}
</ul>
)}
</Droppable>
</DragDropContext>
);
};
export default DragAndDropList;
ReactJS MCQ Questions
Apart from React interview questions for experienced, you also need to prepare for MCQs. Here are some important React JS MCQs:
29. What is React primarily used for in web development?
A. Server-side scripting
B. Database management
C. User interface (UI) development
D. Network protocols
Answer: C. User interface (UI) development
30. In React, which hook is used for performing side effects in functional components?
A. useState
B. useEffect
C. useContext
D. useRef
Answer: B. useEffect
31. In React, what is the purpose of the render method in class components?
A. To handle side effects
B. To define the initial state
C. To return the component’s UI
D. To unsubscribe from event listeners
Answer: C. To return the component’s UI
32. What does JSX stand for in the context of React?
A. JavaScript XML
B. JavaScript Extended
C. JavaScript Syntax Extension
D. JavaScript XML Syntax
Answer: A. JavaScript XML
33. Which of the following libraries is commonly used for state management in React applications?
A. React Router
B. Redux
C. Axios
D. Jest
Answer: B. Redux
Tips to Answer Interview Questions on React JS
If you want to ace your React JX interview, follow these tips:
- Get a solid grip on the basics of React
- Practice coding challenges to sharpen your skills
- Be ready to talk about your React projects
- Know React’s component lifecycle methods
- Expect questions about teamwork and problem-solving
- Don’t be shy and ask questions about the company and tech stack
Conclusion
You’re now well-equipped with the knowledge needed to shine in your React JS interview. These React JS interview questions and answers will boost your confidence and help you make a good impression. If you’re on the hunt for IT jobs, visit Hirist. Hirist is a fantastic platform for job seekers in the IT industry, offering a wide array of opportunities to advance your career. Explore exciting job prospects on Hirist today!